This invention relates to an arm mechanism of a pushbutton type tuner.
A pushbutton type tuner is a tuner, in which one among several predetermined frequencies is selected by inserting a core linked with a memory slide to a corresponding position in a tuning coil, whereby displacement of the memory slide is adjusted by adequately varying the angular position of a setting plate mounted on an arm so as to press the memory slide, which setting plate is fixed after adjustment.
In such a pushbutton type tuner, in order to fix the setting plate to an arm at a desired angular position, heretofore a structure as indicated in FIG. 1 has been utilized. In this structure, on the upper surface of an arm 1 a setting plate 3 is mounted rotatably by using a setting pin 2 having a frange at its upper end. A boss 4 having a circular periphery is formed in one body on the lower surface of the setting plate 3. The periphery of this boss 4 is surrounded by a plate spring 5 having an approximately U-shape. By pressing this plate spring 5 on both the sides by using a pushbutton, the periphery of the boss 4 is tightly grasped by the plate spring 5 so that the setting plate 3 fixed to the arm at a desired angular position cannot rotate around the setting pin 2.
In such an arm mechanism, since the setting plate 3 is pressed laterally from right and left by the plate spring 5, the overall thickness of the arm mechanism may be reduced and thus contributes considerably to miniaturization and thinning of the pushbutton type tuner. However, utilization of such an arm mechanism in a pushbutton type tuner has given rise to following inconveniences.
That is, since the setting plate 3 should be mounted rotatably with respect to the setting pin 2, certain space rests necessarily between the setting pin 2 and the wall of the hole formed for it in the setting plate 3. Consequently this space has given rise to some shakiness and it has been feared that the position of the setting plate with respect to the arm when the setting plate rotated was different from that observed when it rested. If the position of the center of the setting plate is not well fixed, it is difficult to position exactly the setting plate in accordance with the frequency to be selected. Displacement of the center provokes displacement in frequency and thus lowers considerably the quality of the tuner.
In order to remove these inconveniences, it can be supposed to eliminate the shakiness by pressing the setting plate 3 always in one direction, for example toward the base side of the arm 1, so that the setting pin 2 and the wall of the hole in the setting plate 3 is in contact always at a well defined position, when the setting plate 3 is pressed by the plate spring.
However, it has been extremely difficult to press the setting plate 3 only in one direction by using one plate spring 5 while fixing it with a high reliability so that the setting plate 3 once fixed never rotates. Specifically, in order to press the setting plate 3 only in one direction, contact position of the setting plate 3 with the plate spring can be disposed only in the pressing direction and contact area is correspondingly reduced. Therefore, even if shakiness is prevented, the small contact area gives rise to a disadvantage that the setting plate is inadvertently rotated. Of course, when pressing force exerted by the plate spring 5 is extremely strong, even if the setting plate is pressed only in one direction, it can be fixed with a high reliability. However, since pressing force by such a plate spring 5 is based on the force required at the moment when a pushbutton surmounts two tapered parts disposed at the base part of the plate spring, the pressing force caused by the plate spring is limited by the fact that the mounting operation of the pushbutton should be effected smoothly. The pressing force has, therefore, not been able to be increased imprudently.